I agree that the DS was a great platform for RPGs. There are a lot to choose from. My list:

1. Radiant Historia - You are wrong Wolf, this is better than TWEWY
2. The World Ends With You
3. Final Fantasy Tactics A2
4. Mario & Luigi: Bowser's Inside Story
5. Kingdom Hearts: 358/2 Days

Honorable mention: Fire Emblem Shadow Dragon, Golden Sun Dark Dawn, Mario & Luigi Partners in Time, Pokemon Black & White, FF Four Heroes of Light.